Re: [PATCH 1/8] x86, mce: stop calling del_timer_sync() from interrupt

Borislav Petkov
2011-06-17T13:56:57Z

On Fri, Jun 17, 2011 at 04:40:36AM -0400, Hidetoshi Seto wrote:
> Function del_timer_sync() has WARN_ON(in_irq()) in it because
> calling it from interrupt context can cause deadlock if it
> interrupts the target timer running.

No need to explain the del_timer_sync() code here - just say that it's
not allowed to call it from an IRQ context.

> In MCE code, del_timer_sync() is used with on_each_cpu() in
> some parts for sysfs files:

... for the following sysfs files:

> bank*, check_interval, cmci_disabled and ignore_ce.
>
> However use of on_each_cpu() results in calling the function
> passed as the argument in the interrupt context. It means you
> can see a flood of warnings from del_timer_sync() by a simple
> file access, for example:
>
> echo 300 > /sys/devices/system/machinecheck/machinecheck0/check_interval

Good.

>
> Fortunately these MCE specific files are rare-used and AFAIK

rarely used

> only few MCE geeks experience this warning on write.

MCE geeks ??? I wonder who those are :-)

> To remove the warning (for my happy hacking), move timer deletion
> outside of the interrupt context ;-)
>
> v2: update patch description
>
> Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
> ---
> arch/x86/kernel/cpu/mcheck/mce.c | 22 ++++++++++++++++------
> 1 files changed, 16 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
> index 08363b0..42fc8d2 100644
> --- a/arch/x86/kernel/cpu/mcheck/mce.c
> +++ b/arch/x86/kernel/cpu/mcheck/mce.c
> @@ -1140,6 +1140,17 @@ static void mce_start_timer(unsigned long data)
> add_timer_on(t, smp_processor_id());
> }
>
> +/* Must not be called from interrupt where del_timer_sync() can deadlock */
> +static void mce_timer_delete_all(void)
> +{
> + int cpu;
> +
> + for_each_online_cpu(cpu) {
> + if (mce_available(&per_cpu(cpu_info, cpu)))
> + del_timer_sync(&per_cpu(mce_timer, cpu));
> + }
> +}

You're adding the mce_available(..) check just to remove it in the next
patch. Since all those sysfs nodes are behind such a check, there's no
need for it here too.

> static void mce_do_trigger(struct work_struct *work)
> {
> call_usermodehelper(mce_helper, mce_helper_argv, NULL, UMH_NO_WAIT);
> @@ -1750,7 +1761,6 @@ static struct syscore_ops mce_syscore_ops = {
>
> static void mce_cpu_restart(void *data)
> {
> - del_timer_sync(&__get_cpu_var(mce_timer));
> if (!mce_available(__this_cpu_ptr(&cpu_info)))
> return;
> __mcheck_cpu_init_generic();
> @@ -1760,16 +1770,15 @@ static void mce_cpu_restart(void *data)
> /* Reinit MCEs after user configuration changes */
> static void mce_restart(void)
> {
> + mce_timer_delete_all();
> on_each_cpu(mce_cpu_restart, NULL, 1);
> }
>
> /* Toggle features for corrected errors */
> -static void mce_disable_ce(void *all)
> +static void mce_disable_cmci(void *data)
> {
> if (!mce_available(__this_cpu_ptr(&cpu_info)))
> return;
> - if (all)
> - del_timer_sync(&__get_cpu_var(mce_timer));
> cmci_clear();
> }
>
> @@ -1852,7 +1861,8 @@ static ssize_t set_ignore_ce(struct sys_device *s,
> if (mce_ignore_ce ^ !!new) {
> if (new) {
> /* disable ce features */
> - on_each_cpu(mce_disable_ce, (void *)1, 1);
> + mce_timer_delete_all();
> + on_each_cpu(mce_disable_cmci, NULL, 1);
> mce_ignore_ce = 1;
> } else {
> /* enable ce features */
> @@ -1875,7 +1885,7 @@ static ssize_t set_cmci_disabled(struct sys_device *s,
> if (mce_cmci_disabled ^ !!new) {
> if (new) {
> /* disable cmci */
> - on_each_cpu(mce_disable_ce, NULL, 1);
> + on_each_cpu(mce_disable_cmci, NULL, 1);
> mce_cmci_disabled = 1;
> } else {
> /* enable cmci */
> --
> 1.7.1

--
Regards/Gruss,
Boris.

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